That's a tough one. It depends on where you are in your relationship with each other. Are you at least on friendly term? Is she angry? Do you talk on a regular basis?
I think I would probably call or text a simple "how are you doing today?" Just acknowledge that it's a tough day for your wife and you haven't forgotten. DON'T get sappy, just ask how she's doing.
Me 36 Husband 35 D5 S2 separated: 10/29/07-present Served divorce papers 1/22/09 "When the world gives out beneath your feet, it is time to learn how to fly."